Yes, lenses are usually specified as having a minimum and maximum 'f' stop rating; the 'f' stop is a measure of how efficiently the lens allows light from the scene, to pass through the lens and onto the camera CCD sensor. The maximum aperture (when the lens is fully open), is the minimum 'f' stop number and the minimum aperture, (just before the lens completely closes) is the maximum 'f' stop number.

A low minimum 'f' stop number means that the lens can pass more light through during dark conditions, which will produce better pictures at night.

A high maximum 'f' stop number may be necessary where there is a high level of light or reflection. This will prevent the camera ‘whiting out’.